APPLICATION OF TIME-DEPENDENT RAMAN THEORY TO RAMAN EXCITATION PROFILES OF HEXAMETHYLBENZENE-TETRACYANOETHYLENE ELECTRON-DONOR ACCEPTOR COMPLEX

Raman excitation and absorption profiles were obtained for the 1:1 electron donor-acceptor complex of hexamethylbenzene with tetracyanoethylene in dichloromethane solution, The absorption and Raman profiles were analyzed using the time-dependent theory of Heller to obtain the displacements and non-Condon factors for the four strongest Raman modes, the electronic excitation energy, the transition dipole, and solvent line-broadening parameters. The results are compared to the data reported by Myers et al (J, Am. Chem, Sec. 1992, 114, 6208) for the same complex in carbon tetrachloride solution. Attempts to account for solvent effects on the normal-mode displacements in terms of the solvent local field lead are complicated by the effect of the solvent on the structure of the complex, We propose that in CH2Cl2 but not in CCl4, the complex adopts a low-symmetry ground-state geometry which permits vibronic coupling of the charge-transfer and locally excited (TCNE) states.